When page is not NULL, function is called by try_to_unmap_one() with TTU_SPLIT_HUGE_PMD set. There are two cases to call try_to_unmap_one() with TTU_SPLIT_HUGE_PMD set: * unmap_page() * shrink_page_list() In both case, the page passed to try_to_unmap_one() is PageHead() of the THP. If this page's mapping address in process is not HPAGE_PMD_SIZE aligned, this means the THP is not mapped as PMD THP in this process. This could happen when we do mremap() a PMD size range to an un-aligned address. Currently, this case is handled by following check in __split_huge_pmd() luckily. page != pmd_page(*pmd) This patch checks the address to skip some work. Signed-off-by: Wei Yang <richardw.yang@xxxxxxxxxxxxxxx> --- v2: move the check into split_huge_pmd_address(). --- mm/huge_memory.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 893fecd5daa4..2b9c2f412b32 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -2342,6 +2342,22 @@ void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address, pud_t *pud; pmd_t *pmd; + /* + * When page is not NULL, function is called by try_to_unmap_one() + * with TTU_SPLIT_HUGE_PMD set. There are two places set + * TTU_SPLIT_HUGE_PMD + * + * unmap_page() + * shrink_page_list() + * + * In both cases, the "page" here is the PageHead() of a THP. + * + * If the page is not a PMD mapped huge page, e.g. after mremap(), it + * is not necessary to split it. + */ + if (page && !IS_ALIGNED(address, HPAGE_PMD_SIZE)) + return; + pgd = pgd_offset(vma->vm_mm, address); if (!pgd_present(*pgd)) return; -- 2.17.1
